It has long been known in the art that images may be prepared using what is known as a "wash-off" development step in which a latent image is developed by washing with water or other aqueous or non-aqueous developing solution. Such techniques have been widely used in the preparation of flexographic plates, printed circuits, etc. from photosensitive compositions.
It is also known in the art that relief images may be prepared from photosensitive or non-photosensitive elements using wash-off development techniques in which the image layer is applied with an ink jet printer. British Patent 1,431,462 teaches such a method. More specifically, this patent teaches both positive and negative-working systems for forming a relief image using primarily natural proteinaceous materials. In the negative-working system, a polymer coating (e.g. gelatin) is crosslinked, polymerized, or otherwise imagewise hardened by applying a suitable agent (e.g. formaldehyde) using ink jet printing and then dissolving the unhardened areas with a developing solution. In the positive-working system, ink jet printing is used to apply an agent (e.g. enzyme) which will degrade an otherwise insoluble polymer coating, thus rendering it soluble in the developing solution.
Although desirable in principle, the methods disclosed in the aforementioned British Patent are disadvantageous in practice. First, the natural proteinaceous polymers disclosed in this patent lack many physical characteristics necessary from most relief applications, thus rendering such reliefs of limited practical or commercial utility. Second, crosslinking and degradation reactions are relatively slow, particularly at room temperature, thus decreasing the efficiency of the process. The patent teaches that heat could be applied to facilitate the reaction, but this requires an additional step and presents other complications. Third, many of the crosslinking agents, such as aldehydes, are environmentally disadvantageous. Fourth, the use of photopolymerizable compositions requires an additional exposure step, which increases costs and lowers efficiency. Fifth, many of the developing solutions are organic solvent- based, are highly alkaline, or are maintained at elevated temperatures and thus present additional environmental and safety hazards. Sixth, the latent images generated by such methods are not stable, reducing the utility of the process. Finally, the resolution obtainable from these methods was only marginal and often insufficient for demanding commercial application.
The present invention overcomes many of these disadvantages and provides a process which poses minimal environmental risks, is easy to use and has the capability of producing images of high resolution in a very short period of time.